Sets the unit of the FontSize.
TextUnit can have one of the following values:
0 - An appropriate cross-platform selection. On Macintosh, font units is in points, on Windows it is in pixel size, and on Linux it is a scale Point size. This is a legacy carry-over from the days where the TextSize of 12 was the default and 12 was assumed to be the standard font size on each platform.
1 - Units are pixels.
2 - Units are points.
3 - Units are inches.
4 - Units are millimeters.
This property has no effect on REALbasic older than 2009r4.